JP2968839B2 - Color image forming method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming method, and forms an image by a one-shot color method that obtains an electrostatic latent image corresponding to a color image with a single exposure. About the method.

[Background Art] In response to the increase in information processing capability of computers, there is a strong demand for improved functions of peripheral devices. In printers that convey processed information to humans in printed form,
In order to express more complicated information accurately and intuitively, color printing is required.

A color image forming method using an electrophotographic method has been proposed as a method for answering the above demand. There are two types of methods, a multi-process method and a one-shot method.

The multi-process electrophotographic color process is as follows. Cyan, magenta, and color toners
Prepare yellow and black. First, an electrostatic latent image corresponding to cyan is formed on the surface of the electrophotographic photosensitive member, and a cyan toner image is formed. The cyan toner on the surface of the electrophotographic photosensitive member is transferred to a transfer drum. Magenta, sequentially in the same process,
The yellow and black toner images are superimposed on the transfer drum. When the transfer of the four color toners onto the transfer drum is completed, the toner images are transferred to paper and fixed to obtain a color print image. In this method using a normal color toner, a color toner image for one page is formed and then transferred to paper at a time. Therefore, a transfer drum having a large diameter and a circumference of the length of the paper is required. However, there is a disadvantage that the size becomes large. Further, since the transfer drum rotates four times in accordance with the number of types of color toner, in this example, four times, there is a disadvantage that the printing speed is low. In addition, when the color toner is superimposed on the transfer drum, image quality is remarkably degraded if a positional deviation occurs. Therefore, a high-precision mechanical alignment mechanism is required, so that the apparatus becomes heavy and expensive.

As a method for solving these drawbacks, a one-shot color system using an electrophotographic system has been proposed. For example, Japanese Patent Publication No. 55-27341 discloses a method using a special color toner. The one-shot color system is characterized by using a special toner having a color filter core described below. Characteristic toner is composed of two elements having different functions. one,
The other color filter is a color filter that selectively transmits a color, and the other is a color former that reacts with a developer applied to the surface of a recording sheet to generate a color complementary to the color transmitted through the color filter. The color former is transparent before reacting with the developer. These are three types of special toners composed of a color filter that transmits red, green, and blue, and a color former that produces cyan, magenta, and yellow, which are complementary colors of red, green, and blue, by reacting with a color developer. .

First, the photoreceptor is charged, and the special toner is further attached to the surface of the photoreceptor, and is exposed from the special toner side with light combining red light, green light, and blue light depending on image data. When the exposure is completed, the electrostatic attraction between the photoconductor and the special toner including the color filter transmitting the color of the exposure is reduced. For example, red exposure light passes through a special toner that includes a color filter that transmits red and reaches the surface of the photoconductor,
Reduces the amount of charge on the photoreceptor surface. On the other hand, the special toner including a color filter that transmits green and blue absorbs red, so that the red exposure light does not reach the surface of the photoconductor, and the charge amount on the surface of the photoconductor does not decrease.

Next, in the developing step, only the toner having a weak electrostatic attraction is peeled off from the photoconductor to form a color toner image on the surface of the photoconductor. The special toner remaining on the photoreceptor is transferred to a recording paper coated with a developer and fixed to obtain a color image. As in the above example, when exposure is performed in red, magenta-colored and yellow-colored special toners remain on the surface of the photoreceptor, so these two types of special toners are transferred to paper, and a red image is formed on recording paper. You. By exposing in combination light of different wavelength ranges, images of eight colors including white and black are obtained.

The conventional one-shot color method has the following problems due to the use of a special toner.

(A) The handling of the recording paper is troublesome.

(B) Special toner is expensive.

(C) Dust of the special toner occurs.

(D) The color density of the image is insufficient.

(A) is due to the necessity of special paper having a developer applied to the surface thereof as a recording paper in order to develop a color former of the special toner. With plain paper used in a normal electrophotographic image forming apparatus, the color former does not develop color and an image cannot be obtained. Since special paper is difficult to obtain, it is necessary to improve the holding environment to prevent deterioration of the color developer.

(B) is due to the complicated manufacturing process of the special toner. That is, the special toner is expensive because it is manufactured in a complicated process of forming a core of a color filter for selecting a transmission color and coating the core with a color former.

In (c), the color of the color filter constituting the special toner has a complementary color relationship with the color generated by the color former. Therefore, when the color filter is fixed on the paper in the fixing process, the image becomes black. Due to being designed to remain on the surface. Action is needed to remove this residue.

In (d), the color filter member occupies most of the volume of the special toner, and the ratio of the color former is small.

Japanese Patent Application Laid-Open No. 63-285566 discloses a one-shot method using cyan, magenta, and yellow color toners without a color filter nucleus, but the resulting print has three colors of red, green, and blue. And the number of expression colors is insufficient for a color printer. Further, the one-shot system using red, yellow, and green color toners disclosed in Japanese Patent Publication No. 40-28497 can express only red, yellow, and green, and the number of expression colors is insufficient.

The present invention uses a normal color toner having no color filter nucleus and devises an exposure method, thereby eliminating the above-mentioned problems and achieving a color image by a single exposure with a simple configuration. Obtains an electrostatic latent image, has a large number of expression colors,
An object of the present invention is to provide an electrophotographic image forming method for obtaining a high quality color image on plain paper.

DISCLOSURE OF THE INVENTION In order to achieve the above object, the present invention provides a one-shot color system for forming a color image with a single exposure, in which cyan, magenta,
Using three types of color toners that transmit each color of yellow and emit the same color as the color of the transmitted light, red, green, and blue light whose exposure light energy can be varied are used as color toners on the photoconductor. The method is characterized in that the color toner is selectively separated from the photosensitive member by changing the combination of light of each color and the amount of light energy of exposure.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a), 1 (b) and 1 (c) are explanatory views for explaining the principle of an exposure method according to the present invention, and FIG. 2 is a color for explaining a hue of an expression color of an image. FIG. 3 is a configuration diagram showing the configuration of the electrophotographic image forming apparatus according to the present invention, and FIG. 4 is an explanatory diagram illustrating the transmission spectrum of the color toner and the optical writing wavelength.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 illustrates a method for controlling an electrostatic force between a color toner and an electrophotographic photosensitive member according to the exposure method of the present invention.

The electrophotographic photosensitive member used an organic optical semiconductor layer having sensitivity to red light, green light and blue light. A cyan toner C that charges the surface of the electrophotographic photosensitive member 1 and transmits blue light and green light and absorbs red light, and a magenta toner that transmits blue light and red light and absorbs green light.
M, yellow toner Y that transmits green light and red light and absorbs blue light
Is further uniformly attached to each color. The color toner is mainly composed of a colorant that determines the spectral transmission spectrum of the toner, a binder resin for fixing to the recording paper, and a charge control agent that controls the charging characteristics of the toner. As the colorant, a pigment, a dye, a sublimable dye, or the like is used. The core of the color filter for selecting the transmission color, which is necessary for the special toner described in the section of the conventional problem, is unnecessary in the present invention.

The light intensity I _R , I _G , and I _B are sufficient for the surface potential of the electrophotographic photoreceptor to be sufficiently increased when light is written on the electrophotographic photoreceptor on which toner is formed using red, green, and blue light. And the light intensity required to release the toner for each color.
1/2, depending on the transmittance of the color toner, the exposure time, and the sensitivity characteristics of the photoconductor.

 This can be expressed by the following equation.

(2 × I _R ) × T _R × Δt = E _R , (2 × I _G ) × T _G × Δt = E _G , (2 × I _B ) × T _B × Δt = E _B where T _R , T _G, T _B is described later in detail, a transmittance of the light of the color toner, Delta] t is the exposure time, E _R,
E _G and E _B are red, green, and blue light, respectively, and when the electrophotographic photosensitive member to which the color toner is not adhered is exposed, it is necessary to sufficiently lower the surface potential of the electrophotographic photosensitive member. Light energy for each color.

The meaning of the above relational expression is as follows. Light intensity
I _R, when I _G, is exposed from the side of the color toner at twice the light intensity of I _B, the light intensity I _R, I _G, the value obtained by multiplying the transmittance of the color toner to 2 times the value of I _B Reaching the surface of the electrophotographic photosensitive member,
When this exposure is continued for Δt, the electrophotographic photosensitive member obtains light energy necessary for sufficiently lowering its surface potential.

Next, the wavelengths of the red, green, and blue writing light (exposure) and the transmittance of the color toner of each color will be described with reference to FIG.

The transmission spectrum of the cyan toner is indicated by 12, the transmission spectrum of the magenta toner is indicated by 13, and the transmission spectrum of the yellow toner is indicated by 14. The red exposure is red light with a center wavelength of 640 nm, where the transmittances of magenta toner and yellow toner are almost equal,
The green exposure is performed with green light having a center wavelength of 530 nm where the transmittances of cyan toner and yellow toner are almost equal, and the blue exposure is performed with blue having a center wavelength of 415 nm where the transmittances of cyan and magenta toners are almost equal. .

T _R is the magenta toner and yellow toner, a transmittance of light with a red exposure mentioned above.

_TG is the transmittance of the cyan toner and the yellow toner with respect to light for green exposure. T _B is the cyan toner and magenta toner, a transmittance of light of the blue exposure.

Figure 1 (a) is a case where the exposure with green light of the red light and the light intensity I _G of the light intensity I _R. Since the cyan toner C absorbs red light and transmits only green light, the green light reaches the surface of the electrophotographic photosensitive member, slightly reduces the electric charge on the surface of the electrophotographic photosensitive member, and causes the cyan toner C and the electrophotographic photosensitive member to have a low charge. Reduce the electrostatic force between them slightly. However, the light intensity I _G is a cyan toner in the developing step to a degree sufficient to peel from the electrophotographic photosensitive member, because half of the amount of exposure necessary to cause the lowering of the electrostatic force, the cyan toner electrophotographic photosensitive member And is not peeled off in the developing process. The magenta toner M absorbs green light and transmits only red light. So half of the amount of exposure required for the light intensity I _R gives a reduction in sufficient electrostatic force magenta toner in the developing step in peeling from the electrophotographic photosensitive member, a magenta toner peeled from the electrophotographic photosensitive member in the developing step Not done.

On the other hand, since the yellow toner Y transmits both green light and red light, the surface of the electrophotographic photosensitive member under the yellow toner Y is exposed with both green light and red light. The two toners, one half the amount of exposure light required to give a sufficient reduction in electrostatic force to peel off the yellow toner from the electrophotographic photosensitive member, reach the surface of the electrophotographic photosensitive member. Provides a sufficient reduction in electrostatic force to peel off from the photoreceptor.

That is, the color toner that transmits only one of the two types of exposure wavelength light is not separated from the electrophotographic photosensitive member in the developing process, and only the color toner that transmits both wavelength light is transmitted from the electrophotographic photosensitive member in the developing process. Peeled off.

When exposed with blue light of the red light and the light intensity I _B of the light intensity I _R, since only the magenta toner transmits light in both the red light and blue light, only the electrostatic force between the electrophotographic photosensitive member and the magenta toner Greatly decreases, and only magenta toner
It can be easily peeled off from the surface of the electrophotographic photosensitive member.

When exposed with blue light green light and the light intensity I _B of the light intensity I _G, since only the cyan toner to transmit light in both the green and blue light,
The electrostatic force of the cyan toner alone is greatly reduced, and only the cyan toner can be easily separated from the surface of the electrophotographic photosensitive member in the developing step.

That is, when monochromatic exposure is performed with two wavelengths of light having an amount of light that is half of the amount of exposure required to sufficiently reduce the electrostatic force, only one type of color toner that transmits the two wavelengths of exposure is selected. Easily separated from the electrophotographic photosensitive member in the developing step.

Next, a method for selecting two types of color toners will be described. In Fig. 1 (b), shows the case of exposing the electrophotographic photoreceptor from a color toner side red light of the light intensity 2 × I _R. Since the cyan toner C absorbs red light, the surface potential of the electrophotographic photosensitive member under the cyan toner hardly decreases. The surface potential of the electrophotographic photosensitive member under the magenta toner M and the yellow toner Y transmitting the red light is greatly reduced. Light intensity 2 ×
I _R is peeled from the toner in the developing step is a sufficient amount to produce a reduction in sufficient electrostatic force to peel from the electrophotographic photosensitive member, the magenta toner M and yellow toner Y by the developing process from an electrophotographic photosensitive member it can.

When exposed with green light of a light intensity 2 × I _G, decreases the electrostatic force between the electrophotographic photosensitive member of the cyan toner and yellow toner which transmits the green light, can be easily peeled off from the electrophotographic photosensitive member in the developing step, transmits green light Only the unreacted magenta toner remains on the surface of the electrophotographic photosensitive member.

When exposed with blue light of the light intensity 2 × I _B S, reduces the electrostatic force between the electrophotographic photosensitive member of the cyan toner and magenta toner which transmits blue light, can be easily peeled off from the electrophotographic photosensitive member in the developing step, Only the yellow toner that does not transmit blue remains on the surface of the electrophotographic photosensitive member.

In other words, when monochromatic exposure is performed at a light intensity that sufficiently reduces the electrostatic force, two types of color toners that transmit the color of the exposure are selected and easily separated from the electrophotographic photoreceptor in the development process, and the color of the exposure is reduced. One type of color toner that does not pass through remains on the surface of the electrophotographic photosensitive member.

Next, to select all three color toners,
As shown in FIG. 1 (c), the light intensity I _R red light, the light intensity I _G
Green light, and exposure in the blue light of the light intensity I _B of. As described above, the light intensity of the exposure of each color does not sufficiently decrease the electrostatic force with a single color, but when exposed with at least two colors, the electrostatic intensity decreases sufficiently to peel off the toner in the developing process. The intensity of the light to be generated. The electrophotographic photosensitive member under the cyan toner C is irradiated with blue light and green light, and causes a reduction in electrostatic force enough to be peeled off in the developing process. The electrophotographic photoreceptor under the magenta toner M is irradiated with blue light and red light, and causes a reduction in electrostatic force enough to be peeled off in the developing process. The electrophotographic photoreceptor under the yellow toner Y is irradiated with green light and red light, and causes a decrease in electrostatic force enough to be peeled off in the developing process. That is, all three types of color toners can be easily separated from the electrophotographic photosensitive member in the developing step.

The color toner separated from the electrophotographic photoreceptor in the developing process is transferred to recording paper in the transferring process, spreads two-dimensionally in the fixing process, and the color toners overlap and mix colors.

In summary, the type and intensity of light to be exposed,
Type of color toner peeled off from the electrophotographic photoreceptor in the development process,: color of image when the peeled color toner is transferred and fixed,: type of color toner remaining on the electrophotographic photoreceptor,: electrophotographic photoreceptor Table 1 shows the relationship between the colors of the image when the remaining color toner is transferred and fixed.

The color of the image obtained by transferring and fixing the color toner separated from the electrophotographic photosensitive member and the color of the image obtained by transferring and fixing the color toner remaining on the electrophotographic photosensitive member have a complementary color relationship. In any case, an image of eight colors is obtained including white and black.

Light exposure, the light intensity I _R, it is necessary I _G, I _B and 2 times the light intensity thereof. There are a method of changing the light intensity of the optical writing and a method of changing the light writing time. When the optical writing device is a self-luminous type such as a laser and performs point scanning, the light intensity itself is changed, or the light emitted from the laser is changed using a light modulator.
The light emission time may be changed while the light emission intensity is kept constant.
In the case of a self-luminous type such as an LED or a fiber optical tube and an array type, the luminous intensity of luminous dots constituting the array is changed. The light emission time may be changed while the light emission intensity is kept constant. In the case of a shutter type such as a liquid crystal shutter or a PLZT (lead-lanthanum-zirconate-titanate) thio shutter, the transmittance of pixels constituting the shutter is changed. The light transmittance may be changed with time while the transmittance of the shutter pixel is kept constant.

(Example 2) Intermediate colors other than the respective colors of blue, cyan, green, yellow, red and magenta can be obtained by the following three methods. The first method is a method using area gradation using a plurality of dots, although the resolution of the pixel is reduced. One picture element is composed of a plurality of dots, for example, 4 × 4 dots. In accordance with the color to be represented by the picture element, cyan, magenta and yellow color toners are independently arranged in 4 × 4 dots. When one picture element is composed of 4 × 4 = 16 dots, cyan, magenta, and yellow can be expressed in 16 gradations each with one picture element, so that 4096 kinds of colors can be expressed by one picture element. Construct a picture element, 4 × 4 in this example
= 16 dots are cyan toner, magenta toner,
Either three cases of any one type of yellow toner, three cases of any two types, three types of all types, and none of all types are provided. Since these eight cases correspond to the eight colors described above, an intermediate color can be obtained by the basic exposure method shown in Table 2.

The second method is to express an intermediate color by performing area gradation for each color within one dot. In the first method described above, for one dot, each color toner is 1
There are only two states: the entire area of the dot or none at all. In the second method, there is also an intermediate state, that is, a state where a certain percentage of the area of one dot is attached. This second method can be embodied by a digital method and an analog method. The digital method is a method in which the shape of exposure light is made smaller than one dot, the time during which the photoconductor moves by one dot is further divided, and the exposure time is controlled in units of the divided time. . After the color of the toner to be selected is determined, the exposure light is determined according to Table 1, and the exposure time is controlled for each exposure color according to the ratio of the Y, M, and C toners. For example, one dot area 50%
When the yellow toner is selected for magenta toner and 30% of the area of one dot is selected, 30% of the time required for the electrophotographic photosensitive member to move by one dot is used for the exposure shown in (4) of Table 1 for Y. , M toner, and only the Y toner should be selected in the exposure of (1) in Table 1 for 20% of the time.

The analog approach is as follows. The location distribution of light energy obtained by integrating exposure light within one dot is a Gaussian distribution having a light energy peak at the center position of one dot. By setting the threshold value to an appropriate light energy value, it becomes possible to change the image area of the color toner for each dot depending on the light intensity of exposure. For example, the light intensity _{I R (I G, I B} ) can not in the color toner image, the light intensity _{2 × I R (2 × I} G, 2 × I B), 1
An electrophotographic process can be designed such that an image of a color toner is formed on almost the entire area of the dot, and an intermediate light intensity changes the area where the color toner image is formed depending on the light intensity. This is a process used in analog color copiers. By exposing with two wavelengths of light and changing the ratio of the light intensity of the two wavelengths of light, the color of the image obtained when only one wavelength of light is exposed with strong light and only the other wavelength of light are A color intermediate between the colors of the image obtained when exposed to intense light is obtained.

In Table 2, when exposed with red light and green light, the intensity of light to be exposed, the intensity of light reaching the surface of the electrophotographic photoreceptor under each color toner, and the light intensity and color toner form an image Ratio to the minimum light intensity required for: the type of color toner to be peeled from the electrophotographic photoreceptor,
The color of the image when the peeled color toner is transferred and fixed is shown for a typical ratio of the light intensity of red light and green light. When the value in the column is larger than 1, the color toner is peeled off from the surface of the electrophotographic photoreceptor, and the area of the peeled portion depends on the value in the column. Mourn. (0.5) means that the color toner occupies half the area of one dot. As the intensity of green light increases, the color of the image becomes red, orange,
Changes to yellow, yellow-green, and green.

Table 3 shows, in the same format as in Table 2, the colors of the image when exposed by combining green light and blue light, and blue light and red light. The symbols (a) to (f) in the columns of Table 2 and Table 3
The position in the CIE chromaticity diagram of the figure is shown.

By the exposure method described above, a color composed of two types of color toners can be obtained.

To further expand the range of color representation of the image, the image may be composed of three types of color toners. Table 4 shows the colors of the images when exposed with light combining red, green, and blue light in the same format as in Tables 2 and 3. However, the columns in Tables 2 and 3 are omitted here. In Table 4,
While the sum of the light intensities of the three wavelength lights was kept constant, the red light and the green light were made to have the same light intensity, and the light intensity ratio of each light was changed.

A third method for expressing an intermediate color is a combination of the first method and the second method. Since a picture element is composed of a plurality of dots while producing an intermediate color with one dot, a more subtle color can be expressed.

(Example 3) In Example 1, eight colors were obtained by a subtractive color mixture method. In this embodiment,
Assuming that the three basic colors are three colors, the three colors are additively mixed to produce a further three colors.
This is a method of forming colors and obtaining a total of eight colors including white and black. As shown in FIG. 1 (b), exposure is performed using light of one kind of wavelength range to obtain three basic colors. The results are (4), (5) and (6) in Table 1.

When an image is formed with the color toner peeled off from the electrophotographic photosensitive member in the developing step, red, green, and blue are obtained as three basic colors as shown in the column of Table 1. The three basic colors are additively mixed to produce cyan, magenta, and yellow. 1
The dots are divided into 1/2 dots, and three different basic colors are arranged for each ド ッ ト dot. Alternatively, one picture element is composed of two dots, and three different basic colors are arranged in each dot. For example, if red and green are arranged adjacent to each other and mixed in an additive manner, the color becomes yellow. Although the image becomes darker than when a yellow image is formed only with the yellow toner, the color can be sufficiently identified. If red and blue are arranged adjacently, magenta can be expressed by additive color mixture, and if blue and green are arranged adjacently, cyan can be expressed.

Red light of the light intensity 2 × I _R, green light of the light intensity 2 × I _G, the light intensity 2
× I at least two blue light of either choose to exposure wavelength light _B, as shown in FIG. 1 (c), green light + light intensity of the red light + light intensity I _G of the light intensity I _R is exposed in the light of the blue light of the I _B,
Get black. White without exposure. In the above way cyan,
Eight colors of magenta, yellow, red, green, blue, white and black are obtained.

When the color toner remaining on the electrophotographic photoreceptor is transferred and fixed after completion of the developing process to form an image, the three basic colors are cyan, magenta, and yellow as shown in the column of Table 1. is there. The three basic colors are additively mixed and red,
Make green and blue. For example, cyan and magenta are arranged adjacent to each other, and when added and mixed, the color becomes blue. Compared with blue obtained by subtractive color mixing by arranging cyan and magenta in a superimposed manner, although the chroma is low, the color can be sufficiently identified. If magenta and yellow are adjacently arranged, red can be expressed by additive color mixture, and if cyan and yellow are arranged adjacently, green can be expressed.

Red light of the light intensity 2 × I _R, green light of the light intensity 2 × I _G, the light intensity 2
× I at least two blue light of either choose to exposure wavelength light _B, as shown in FIG. 1 (c), green light + light intensity of the red light + light intensity I _G of the light intensity I _R is exposed in the light of the blue light of the I _B,
Get white. Black without exposure. In the above way cyan,
Eight colors of magenta, yellow, red, green, blue, white and black are obtained.

Example 4 FIG. 3 shows a configuration of an electrophotographic color printer using the above-described exposure method as an exposure step. The entire surface of the OPC photosensitive drum 2 having a punk romantic spectral sensitivity characteristic is charged by the charger 3.

In order to form a good electrostatic latent image with the exposure method of the present invention, the photosensitive drum needs to have a sufficiently sharp latent image γ characteristic. As described in detail in the first embodiment, for example, the light intensity
When exposed with a blue red and the light intensity I _B of I _R, but red light and blue light reaches the surface of the photoreceptor under the magenta toner passes through the magenta toner, the photoreceptor under the cyan toner Only blue light and only red light reach the photoreceptor below the yellow toner. In order to obtain a good image, it is desirable that the surface potential of the photoconductor under the magenta toner is sufficiently reduced, and the surface potential of the photoconductor under the cyan toner and the yellow toner is hardly reduced. The light intensity transmitted through the color toner and reaching the surface of the electrophotographic photosensitive member is 2 in light intensity ratio between the selected color toner and the non-selected color toner. Therefore, in order to obtain a high quality image, the contrast ratio of light reaching the surface of the electrophotographic photosensitive member must be 2
In this case, it is desirable that the photoreceptor has a γ characteristic capable of obtaining a sufficiently large surface potential difference. For example, as a photoconductor,
The digital light input photosensitive member disclosed in Japanese Patent Application Laid-Open No. 1-169454 is effective.

Next, a cyan toner, a magenta toner, and a yellow toner are formed as a single toner layer on the surface of the photosensitive drum 2 by the color toner attaching device 4 on the charged photosensitive member. In order to form only one color toner, it is effective to coat the surface of the color toner with a conductive film such as copper iodide and to make the surface of the color toner conductive.

The image data is subjected to data processing in the image processing unit 5 and converted into a signal for driving the optical writing head 6. The optical writing head used a liquid crystal shutter. To independently control red light, green light, and blue light with a liquid crystal shutter, for example, as disclosed in JP-A-59-137930, red light, green light,
A color filter that transmits blue light may be provided for each liquid crystal pixel forming the liquid crystal shutter, and the light transmittance of the liquid crystal pixel may be controlled independently. In JP-A-59-137930, red light,
Liquid crystal pixels having color filters that transmit green light and blue light are provided one by one in the moving direction of the photosensitive drum. In this embodiment, in order to increase the printing speed, red light, green light,
Two liquid crystal pixels each having a color filter that transmits blue light are arranged in the moving direction of the photosensitive drum for each of the transmitted colors.

Color printing on A4 paper at a dot resolution of 300 dpi requires 7680 liquid crystal pixels, three times the number of 2560 liquid crystal pixels required for optical writing by a black and white printer. When the liquid crystal pixels are statically driven, many drive ICs are required, so that the volume and cost of the optical writing head increase.
To reduce the number of drive ICs, it is effective to drive the liquid crystal pixels in a time-division manner. To use light energy effectively,
A liquid crystal capable of storing an optical state when driven in a time-division manner is suitable. If the response speed of the liquid crystal pixels is high, high-speed printing can be performed. For this reason, a ferroelectric liquid crystal having a high-speed response and a memory effect was used.

Further, as disclosed in JP-A-61-52630, driving the ferroelectric liquid crystal with an analog voltage changes the light transmittance to an intermediate state between perfect transmission and non-transmission. It can be controlled in an analog manner. In this embodiment, the respective charges corresponding to the positive analog voltage and the negative analog voltage for driving the liquid crystal pixels are separately stored in capacitors provided for each output terminal in the drive IC, and synchronized with the drive timing. After switching, the liquid crystal pixels were driven by connection to a buffer amplifier provided for each output terminal in the drive IC.
Exposure according to the image data with the liquid crystal shutter head,
Controlling the charge of the photoreceptor under the selected color toner,
The electrostatic force between the selected color toner and the photoreceptor was controlled. The light intensity I _{R of the} exposure was such that the liquid crystal pixels were half-opened, and the light intensity 2 × I _R of the exposure was such that the liquid crystal pixels were fully open, and a difference was provided in the amount of exposure light. Further, the intermediate light intensity was obtained by changing the analog voltage applied to the liquid crystal pixels. Also,
An intermediate value of light intensity was also obtained by the time gradation method. The liquid crystal pixels are only in the two states of fully open or closed, and the liquid crystal pixels are in the light transmitting state for half the time that the electrophotographic photosensitive member moves by one line, and the remaining half of the time. During the time, the liquid crystal pixels were kept closed. Further, an intermediate light intensity was obtained by changing the ratio of the time during which the liquid crystal pixel was in a light transmitting state to the time in which the liquid crystal pixel was not transmitting light. Further, by combining the time gray scale and the analog gray scale, the exposure light amount can be more finely controlled.

The color toner having the reduced electrostatic force was transferred to the charged transfer drum 7, transferred to the recording paper 9 using the transfer corona unit 8, and fixed to the paper by the heat fixing unit 10. The color toner remaining on the surface of the photoconductor 2 without being separated from the photoconductor 2 was scraped off by the cleaner 11. The scraped color toner was sent to the color toner attaching device 4 and reused. Instead of transferring the image to the recording paper via the transfer drum 7, the image may be directly transferred to the recording paper without using the transfer drum.

Although the image is formed using the color toner whose electrostatic force with the electrophotographic photosensitive member has been reduced, the image may be formed using the color toner remaining on the surface of the electrophotographic photosensitive member after the development process. However, since the complementary color of the color of the exposed light becomes an image, it is necessary to reverse the opening and closing of the liquid crystal pixels with the signal for driving the optical writer by using the color toner peeled from the electrophotographic photosensitive member. is there.

Since the consumption amounts of the three types of color toners are different, the ratio of the amount of each color toner in the color toner attaching device 4 changes as the number of prints increases. The amount of each color toner in the color toner attaching device 4 was measured using a light emitting diode and a light receiving sensor, and the color toner was automatically replenished so that the ratio between the color toners became constant.
Calculate the consumption of each color toner from the print data,
You may replenish.

The optical writing by the liquid crystal shutter of the present embodiment may be performed by a color fiber optical tube. Also, a method may be used in which the light emitted from the white gas laser is decomposed into red, green, and blue, and scanning and writing are performed using polygons.
Further, a combination of a semiconductor laser and a harmonic generator may be used. That is, a wavelength of 1.06 μm obtained by exciting a YAG laser with a first semiconductor laser emitting red light and a semiconductor laser.
The second semiconductor laser of green emission obtained by passing the laser light through a double harmonic generator and the emission of blue light obtained by passing the emission light of a semiconductor laser having an emission wavelength of 0.83 μm through a double harmonic generator The third semiconductor laser may be exposed by scanning.

According to the present invention, since an image can be formed by one-shot exposure, a transfer drum for transferring a toner image is not required,
Since high-precision mechanical alignment is not required, the device is small and lightweight. In addition, since a normal color toner which does not require a color filter core is used as the color toner instead of a special color toner, plain paper which does not require special paper and can be easily obtained and stored can be used. In addition, since one-shot optical writing is performed using an optical writing head with no moving parts and high dot position accuracy, an electrophotographic color printer capable of printing high quality color images with high image position accuracy is obtained. be able to.

Claims (3)

(57) [Claims] An electrophotographic photosensitive member is coated with a plurality of light-transmitting color toners of a plurality of colors, exposed from the side of the color toner, developed, and then transferred to a transfer drum or recording paper at one time. In a color image forming method for obtaining an image,
As the color toners, three types of color toners, each transmitting cyan, magenta, and yellow, and emitting the same color as the color of the transmitted light, are used, and the amount of light energy of exposure can be changed to red, green, and blue. A color image forming method, wherein the color toner is selectively separated from the photoreceptor by irradiating the color toner on the photoreceptor and changing the combination of light of each color and the amount of light energy of exposure. 2. When the cyan, magenta or yellow toner transmitting each color is exposed to light of each color of red, green and blue, the amount of light energy required to separate each toner from the photoreceptor is determined. 2. The color image forming method according to claim 1, wherein the amount of light energy for exposure is changed by combining light having a light intensity having a unit of 1/2 of the light intensity of each light to be given. 3. A red light having a center wavelength having the same transmittance of the magenta toner and the yellow toner, a green light having a center wavelength having the same transmittance of the cyan toner and the yellow toner, and a cyan toner having a center wavelength of the cyan toner. 2. The color image forming method according to claim 1, wherein the exposure is performed using blue light having a wavelength having the same transmittance as that of the magenta toner.